In recent years, on-body sensing has been made possible due to the technological progress within sensor miniaturization, energy saving and wireless communications. A sensing device in the form of a body-worn accelerometer-based activity monitor (AM) is able to record motion-induced acceleration signals. From such acceleration signals, activity-context information, such as physical activity related energy expenditure (AEE), activity type and durations can be extracted. In healthcare applications, the activity-context information helps to correctly interpret patients' vital body signals, such as ECG and respiration rate, and to improve the diagnosis. In consumer lifestyle applications, it enables users to maintain a healthy physical activity level, thus avoiding inactivity-related diseases.
To translate the acceleration data into an AEE value with a required accuracy or to be able to provide correct activity type recognition, it may be crucial to have prior knowledge of the sensor's location. The article: “Detection of Sensor Wearing Positions for Accelerometry-based Daily Activity Assessment”, The Sixth LASTED International Conference on Biomedical Engineering, February 2008 by Yin and Goris, discloses a method of detecting a sensor wearing position based on comparing body position dependent features that are extracted from measured acceleration data with features of an established feature database.
FIG. 1 is adapted from the mentioned article by Yin and Goris and shows an example of correlation between the acceleration power accumulated in the form of total accelerations pr. day (y axis) and the corresponding physical activity level measured with a doubly-labeled water method (x axis). The correlation curves 1, 2, 3, which respectively result from linear regression from the experimental data 4, 5, 6, differ depending on the sensor wearing position, i.e., waist 1, 4 (diamond), wrist 2, 5 (square) and bra 3, 6 (triangle). Thus even though the readout data relate to the same activities, the determined physical activity level differ according to the attachment position of the accelerometer.
Hence, there is the need in the art for accurately detecting the wearing position of an on-body sensing device.